Aligning a collimator assembly with led arrays

ABSTRACT

Disclosed herein are techniques for aligning a collimator assembly with an array of LEDs. According to certain embodiments, a method includes using lithography to form a first plurality of contact pads and a second plurality of contact pads on a backplane; bonding a plurality of dies to the first plurality of contact pads, wherein each of the plurality of dies comprises a plurality of light emitting diodes; forming a first plurality of features on the second plurality of contact pads; and aligning a plurality of lenses on an assembly with the plurality of dies by coupling a second plurality of features on the assembly with the first plurality of features on the second plurality of contact pads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to U.S.Provisional Patent Application No. 62/942,324, filed on Dec. 2, 2019,the contents of which are hereby incorporated by reference in theirentirety for all purposes.

BACKGROUND

Light emitting diodes (LEDs) convert electrical energy into opticalenergy, and offer many benefits over other light sources, such asreduced size, improved durability, and increased efficiency. LEDs can beused as light sources in many display systems, such as televisions,computer monitors, laptop computers, tablets, smartphones, projectionsystems, and wearable electronic devices. Micro-LEDs (“μLEDs”) based onIII-nitride semiconductors, such as alloys of A1N, GaN, InN, and thelike, have begun to be developed for various display applications due totheir small size (e.g., with a linear dimension less than 100 μm, lessthan 50 μm, less than 10 μm, or less than 5 μm), high packing density(and hence higher resolution), and high brightness. For example,micro-LEDs that emit light of different colors (e.g., red, green, andblue) can be used to form the sub-pixels of a display system, such as atelevision or a near-eye display system.

SUMMARY

This disclosure relates to aligning a collimator assembly with an arrayof LEDs. According to some embodiments, a method includes usinglithography to form a first plurality of contact pads and a secondplurality of contact pads on a backplane; bonding a plurality of dies tothe first plurality of contact pads, wherein each of the plurality ofdies comprises a plurality of light emitting diodes; forming a firstplurality of features on the second plurality of contact pads; andaligning a plurality of lenses on an assembly with the plurality of diesby coupling a second plurality of features on the assembly with thefirst plurality of features on the second plurality of contact pads.

The first plurality of features may be balls including a fusiblematerial, and the second plurality of features may be recesses in thecollimator assembly. Each of the balls may have a spherical shape.Alternatively, each of the balls may have an oblong shape. Each of theplurality of lenses may be a collimating lens. The first plurality ofcontact pads and the second plurality of contact pads may be formedsimultaneously.

According to some embodiments, a method includes using lithography toform a plurality of contact pads on a backplane and a plurality ofopenings in the backplane; bonding a plurality of dies to the pluralityof contact pads, wherein each of the plurality of dies comprises aplurality of light emitting diodes; and aligning a plurality of lenseson an assembly with the plurality of dies by coupling a plurality offeatures on the assembly with the plurality of openings in thebackplane.

The plurality of features may be protrusions from the collimatorassembly. The plurality of openings may extend through a redistributionlayer of the backplane. The backplane may also include a metal sidewallfor each of the plurality of openings. Each of the plurality of lensesmay be a collimating lens. The plurality of contact pads and theplurality of openings are formed simultaneously.

According to some embodiments, a display projector includes a displaydevice and a collimator assembly. The display device includes abackplane and a plurality of dies. Each die of the plurality of diesincludes a plurality of light emitting diodes, and each die of theplurality of dies is connected to the backplane. The display device alsoincludes a first plurality of features on the backplane. The collimatorassembly includes a plurality of lenses and a second plurality offeatures on the collimator assembly. The first plurality of features onthe backplane are coupled with the second plurality of features on thecollimator assembly such that the plurality of dies are aligned with theplurality of lenses.

The first plurality of features may be balls including a fusiblematerial and the second plurality of features may be recesses in thecollimator assembly. Each of the balls may have a spherical shape.Alternatively, each of the balls may have an oblong shape.

Alternatively, the first plurality of features may be openings in thebackplane and the second plurality of features may be protrusions fromthe collimator assembly. The openings may extend through aredistribution layer of the backplane. The backplane may also include ametal sidewall for each of the openings.

This summary is neither intended to identify key or essential featuresof the claimed subject matter, nor is it intended to be used inisolation to determine the scope of the claimed subject matter. Thesubject matter should be understood by reference to appropriate portionsof the entire specification of this disclosure, any or all drawings, andeach claim. The foregoing, together with other features and examples,will be described in more detail below in the following specification,claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe following figures.

FIG. 1 is a simplified block diagram of an example of an artificialreality system environment including a near-eye display according tocertain embodiments.

FIG. 2 is a perspective view of an example of a near-eye display in theform of a head-mounted display (HMD) device for implementing some of theexamples disclosed herein.

FIG. 3 is a perspective view of an example of a near-eye display in theform of a pair of glasses for implementing some of the examplesdisclosed herein.

FIG. 4 illustrates an example of an optical see-through augmentedreality system including a waveguide display according to certainembodiments.

FIG. 5A illustrates an example of a near-eye display device including awaveguide display according to certain embodiments.

FIG. 5B illustrates an example of a near-eye display device including awaveguide display according to certain embodiments.

FIG. 6 illustrates an example of an image source assembly in anaugmented reality system according to certain embodiments.

FIG. 7A illustrates an example of a light emitting diode (LED) having avertical mesa structure according to certain embodiments.

FIG. 7B is a cross-sectional view of an example of an LED having aparabolic mesa structure according to certain embodiments.

FIG. 8A illustrates an example of a method of die-to-wafer bonding forarrays of LEDs according to certain embodiments.

FIG. 8B illustrates an example of a method of wafer-to-wafer bonding forarrays of LEDs according to certain embodiments.

FIGS. 9A-9D illustrates an example of a method of hybrid bonding forarrays of LEDs according to certain embodiments.

FIG. 10 illustrates an example of an LED array with secondary opticalcomponents fabricated thereon according to certain embodiments.

FIG. 11 illustrates an example of a display device that includes threearrays of LEDs that are coupled to a waveguide.

FIG. 12 illustrates a first example of a method for aligning collimatinglenses with dies that are positioned on a backplane.

FIGS. 13A and 13B illustrate a second example of a method for aligningcollimating lenses with dies that are positioned on a backplane.

FIG. 14 is a simplified block diagram of an electronic system of anexample of a near-eye display according to certain embodiments.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated may be employed without departing from theprinciples, or benefits touted, of this disclosure.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

This disclosure relates generally to light emitting diodes (LEDs). TheLEDs described herein may be used in conjunction with varioustechnologies, such as an artificial reality system. An artificialreality system, such as a head-mounted display (HMD) or heads-up display(HUD) system, generally includes a display configured to presentartificial images that depict objects in a virtual environment. Thedisplay may present virtual objects or combine images of real objectswith virtual objects, as in virtual reality (VR), augmented reality(AR), or mixed reality (MR) applications. For example, in an AR system,a user may view both displayed images of virtual objects (e.g.,computer-generated images (CGIs)) and the surrounding environment by,for example, seeing through transparent display glasses or lenses (oftenreferred to as optical see-through) or viewing displayed images of thesurrounding environment captured by a camera (often referred to as videosee-through). In some AR systems, the artificial images may be presentedto users using an LED-based display subsystem.

As used herein, the term “light emitting diode (LED)” refers to a lightsource that includes at least an n-type semiconductor layer, a p-typesemiconductor layer, and a light emitting region (i.e., active region)between the n-type semiconductor layer and the p-type semiconductorlayer. The light emitting region may include one or more semiconductorlayers that form one or more heterostructures, such as quantum wells. Insome embodiments, the light emitting region may include multiplesemiconductor layers that form one or more multiple-quantum-wells(MQWs), each including multiple (e.g., about 2 to 6) quantum wells.

As used herein, the term “micro-LED” or “μLED” refers to an LED that hasa chip where a linear dimension of the chip is less than about 200 μm,such as less than 100 μm, less than 50 μm, less than 20 μm, less than 10μm, or smaller. For example, the linear dimension of a micro-LED may beas small as 6 μm, 5 μm, 4 μm, 2 μm, or smaller. Some micro-LEDs may havea linear dimension (e.g., length or diameter) comparable to the minoritycarrier diffusion length. However, the disclosure herein is not limitedto micro-LEDs, and may also be applied to mini-LEDs and large LEDs.

As used herein, the term “bonding” may refer to various methods forphysically and/or electrically connecting two or more devices and/orwafers, such as adhesive bonding, metal-to-metal bonding, metal oxidebonding, wafer-to-wafer bonding, die-to-wafer bonding, hybrid bonding,soldering, under-bump metallization, and the like. For example, adhesivebonding may use a curable adhesive (e.g., an epoxy) to physically bondtwo or more devices and/or wafers through adhesion. Metal-to-metalbonding may include, for example, wire bonding or flip chip bondingusing soldering interfaces (e.g., pads or balls), conductive adhesive,or welded joints between metals. Metal oxide bonding may form a metaland oxide pattern on each surface, bond the oxide sections together, andthen bond the metal sections together to create a conductive path.Wafer-to-wafer bonding may bond two wafers (e.g., silicon wafers orother semiconductor wafers) without any intermediate layers and is basedon chemical bonds between the surfaces of the two wafers. Wafer-to-waferbonding may include wafer cleaning and other preprocessing, aligning andpre-bonding at room temperature, and annealing at elevated temperatures,such as about 250° C. or higher. Die-to-wafer bonding may use bumps onone wafer to align features of a pre-formed chip with drivers of awafer. Hybrid bonding may include, for example, wafer cleaning,high-precision alignment of contacts of one wafer with contacts ofanother wafer, dielectric bonding of dielectric materials within thewafers at room temperature, and metal bonding of the contacts byannealing at, for example, 250-300° C. or higher. As used herein, theterm “bump” may refer generically to a metal interconnect used or formedduring bonding.

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofexamples of the disclosure. However, it will be apparent that variousexamples may be practiced without these specific details. For example,devices, systems, structures, assemblies, methods, and other componentsmay be shown as components in block diagram form in order not to obscurethe examples in unnecessary detail. In other instances, well-knowndevices, processes, systems, structures, and techniques may be shownwithout necessary detail in order to avoid obscuring the examples. Thefigures and description are not intended to be restrictive. The termsand expressions that have been employed in this disclosure are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof. The word “example”is used herein to mean “serving as an example, instance, orillustration.” Any embodiment or design described herein as “example” isnot necessarily to be construed as preferred or advantageous over otherembodiments or designs.

FIG. 1 is a simplified block diagram of an example of an artificialreality system environment 100 including a near-eye display 120 inaccordance with certain embodiments. Artificial reality systemenvironment 100 shown in FIG. 1 may include near-eye display 120, anoptional external imaging device 150, and an optional input/outputinterface 140, each of which may be coupled to an optional console 110.While FIG. 1 shows an example of artificial reality system environment100 including one near-eye display 120, one external imaging device 150,and one input/output interface 140, any number of these components maybe included in artificial reality system environment 100, or any of thecomponents may be omitted. For example, there may be multiple near-eyedisplays 120 monitored by one or more external imaging devices 150 incommunication with console 110. In some configurations, artificialreality system environment 100 may not include external imaging device150, optional input/output interface 140, and optional console 110. Inalternative configurations, different or additional components may beincluded in artificial reality system environment 100.

Near-eye display 120 may be a head-mounted display that presents contentto a user. Examples of content presented by near-eye display 120 includeone or more of images, videos, audio, or any combination thereof. Insome embodiments, audio may be presented via an external device (e.g.,speakers and/or headphones) that receives audio information fromnear-eye display 120, console 110, or both, and presents audio databased on the audio information. Near-eye display 120 may include one ormore rigid bodies, which may be rigidly or non-rigidly coupled to eachother. A rigid coupling between rigid bodies may cause the coupled rigidbodies to act as a single rigid entity. A non-rigid coupling betweenrigid bodies may allow the rigid bodies to move relative to each other.In various embodiments, near-eye display 120 may be implemented in anysuitable form-factor, including a pair of glasses. Some embodiments ofnear-eye display 120 are further described below with respect to FIGS. 2and 3. Additionally, in various embodiments, the functionality describedherein may be used in a headset that combines images of an environmentexternal to near-eye display 120 and artificial reality content (e.g.,computer-generated images). Therefore, near-eye display 120 may augmentimages of a physical, real-world environment external to near-eyedisplay 120 with generated content (e.g., images, video, sound, etc.) topresent an augmented reality to a user.

In various embodiments, near-eye display 120 may include one or more ofdisplay electronics 122, display optics 124, and an eye-tracking unit130. In some embodiments, near-eye display 120 may also include one ormore locators 126, one or more position sensors 128, and an inertialmeasurement unit (IMU) 132. Near-eye display 120 may omit any ofeye-tracking unit 130, locators 126, position sensors 128, and IMU 132,or include additional elements in various embodiments. Additionally, insome embodiments, near-eye display 120 may include elements combiningthe function of various elements described in conjunction with FIG. 1.

Display electronics 122 may display or facilitate the display of imagesto the user according to data received from, for example, console 110.In various embodiments, display electronics 122 may include one or moredisplay panels, such as a liquid crystal display (LCD), an organic lightemitting diode (OLED) display, an inorganic light emitting diode (ILED)display, a micro light emitting diode (μLED) display, an active-matrixOLED display (AMOLED), a transparent OLED display (TOLED), or some otherdisplay. For example, in one implementation of near-eye display 120,display electronics 122 may include a front TOLED panel, a rear displaypanel, and an optical component (e.g., an attenuator, polarizer, ordiffractive or spectral film) between the front and rear display panels.Display electronics 122 may include pixels to emit light of apredominant color such as red, green, blue, white, or yellow. In someimplementations, display electronics 122 may display a three-dimensional(3D) image through stereoscopic effects produced by two-dimensionalpanels to create a subjective perception of image depth. For example,display electronics 122 may include a left display and a right displaypositioned in front of a user's left eye and right eye, respectively.The left and right displays may present copies of an image shiftedhorizontally relative to each other to create a stereoscopic effect(i.e., a perception of image depth by a user viewing the image).

In certain embodiments, display optics 124 may display image contentoptically (e.g., using optical waveguides and couplers) or magnify imagelight received from display electronics 122, correct optical errorsassociated with the image light, and present the corrected image lightto a user of near-eye display 120. In various embodiments, displayoptics 124 may include one or more optical elements, such as, forexample, a substrate, optical waveguides, an aperture, a Fresnel lens, aconvex lens, a concave lens, a filter, input/output couplers, or anyother suitable optical elements that may affect image light emitted fromdisplay electronics 122. Display optics 124 may include a combination ofdifferent optical elements as well as mechanical couplings to maintainrelative spacing and orientation of the optical elements in thecombination. One or more optical elements in display optics 124 may havean optical coating, such as an anti-reflective coating, a reflectivecoating, a filtering coating, or a combination of different opticalcoatings.

Magnification of the image light by display optics 124 may allow displayelectronics 122 to be physically smaller, weigh less, and consume lesspower than larger displays. Additionally, magnification may increase afield of view of the displayed content. The amount of magnification ofimage light by display optics 124 may be changed by adjusting, adding,or removing optical elements from display optics 124. In someembodiments, display optics 124 may project displayed images to one ormore image planes that may be further away from the user's eyes thannear-eye display 120.

Display optics 124 may also be designed to correct one or more types ofoptical errors, such as two-dimensional optical errors,three-dimensional optical errors, or any combination thereof.Two-dimensional errors may include optical aberrations that occur in twodimensions. Example types of two-dimensional errors may include barreldistortion, pincushion distortion, longitudinal chromatic aberration,and transverse chromatic aberration. Three-dimensional errors mayinclude optical errors that occur in three dimensions. Example types ofthree-dimensional errors may include spherical aberration, comaticaberration, field curvature, and astigmatism.

Locators 126 may be objects located in specific positions on near-eyedisplay 120 relative to one another and relative to a reference point onnear-eye display 120. In some implementations, console 110 may identifylocators 126 in images captured by external imaging device 150 todetermine the artificial reality headset's position, orientation, orboth. A locator 126 may be an LED, a corner cube reflector, a reflectivemarker, a type of light source that contrasts with an environment inwhich near-eye display 120 operates, or any combination thereof. Inembodiments where locators 126 are active components (e.g., LEDs orother types of light emitting devices), locators 126 may emit light inthe visible band (e.g., about 380 nm to 750 nm), in the infrared (IR)band (e.g., about 750 nm to 1 mm), in the ultraviolet band (e.g., about10 nm to about 380 nm), in another portion of the electromagneticspectrum, or in any combination of portions of the electromagneticspectrum.

External imaging device 150 may include one or more cameras, one or morevideo cameras, any other device capable of capturing images includingone or more of locators 126, or any combination thereof. Additionally,external imaging device 150 may include one or more filters (e.g., toincrease signal to noise ratio). External imaging device 150 may beconfigured to detect light emitted or reflected from locators 126 in afield of view of external imaging device 150. In embodiments wherelocators 126 include passive elements (e.g., retroreflectors), externalimaging device 150 may include a light source that illuminates some orall of locators 126, which may retro-reflect the light to the lightsource in external imaging device 150. Slow calibration data may becommunicated from external imaging device 150 to console 110, andexternal imaging device 150 may receive one or more calibrationparameters from console 110 to adjust one or more imaging parameters(e.g., focal length, focus, frame rate, sensor temperature, shutterspeed, aperture, etc.).

Position sensors 128 may generate one or more measurement signals inresponse to motion of near-eye display 120. Examples of position sensors128 may include accelerometers, gyroscopes, magnetometers, othermotion-detecting or error-correcting sensors, or any combinationthereof. For example, in some embodiments, position sensors 128 mayinclude multiple accelerometers to measure translational motion (e.g.,forward/back, up/down, or left/right) and multiple gyroscopes to measurerotational motion (e.g., pitch, yaw, or roll). In some embodiments,various position sensors may be oriented orthogonally to each other.

IMU 132 may be an electronic device that generates fast calibration databased on measurement signals received from one or more of positionsensors 128. Position sensors 128 may be located external to IMU 132,internal to IMU 132, or any combination thereof. Based on the one ormore measurement signals from one or more position sensors 128, IMU 132may generate fast calibration data indicating an estimated position ofnear-eye display 120 relative to an initial position of near-eye display120. For example, IMU 132 may integrate measurement signals receivedfrom accelerometers over time to estimate a velocity vector andintegrate the velocity vector over time to determine an estimatedposition of a reference point on near-eye display 120. Alternatively,IMU 132 may provide the sampled measurement signals to console 110,which may determine the fast calibration data. While the reference pointmay generally be defined as a point in space, in various embodiments,the reference point may also be defined as a point within near-eyedisplay 120 (e.g., a center of IMU 132).

Eye-tracking unit 130 may include one or more eye-tracking systems. Eyetracking may refer to determining an eye's position, includingorientation and location of the eye, relative to near-eye display 120.An eye-tracking system may include an imaging system to image one ormore eyes and may optionally include a light emitter, which may generatelight that is directed to an eye such that light reflected by the eyemay be captured by the imaging system. For example, eye-tracking unit130 may include a non-coherent or coherent light source (e.g., a laserdiode) emitting light in the visible spectrum or infrared spectrum, anda camera capturing the light reflected by the user's eye. As anotherexample, eye-tracking unit 130 may capture reflected radio waves emittedby a miniature radar unit. Eye-tracking unit 130 may use low-power lightemitters that emit light at frequencies and intensities that would notinjure the eye or cause physical discomfort. Eye-tracking unit 130 maybe arranged to increase contrast in images of an eye captured byeye-tracking unit 130 while reducing the overall power consumed byeye-tracking unit 130 (e.g., reducing power consumed by a light emitterand an imaging system included in eye-tracking unit 130). For example,in some implementations, eye-tracking unit 130 may consume less than 100milliwatts of power.

Near-eye display 120 may use the orientation of the eye to, e.g.,determine an inter-pupillary distance (IPD) of the user, determine gazedirection, introduce depth cues (e.g., blur image outside of the user'smain line of sight), collect heuristics on the user interaction in theVR media (e.g., time spent on any particular subject, object, or frameas a function of exposed stimuli), some other functions that are basedin part on the orientation of at least one of the user's eyes, or anycombination thereof. Because the orientation may be determined for botheyes of the user, eye-tracking unit 130 may be able to determine wherethe user is looking. For example, determining a direction of a user'sgaze may include determining a point of convergence based on thedetermined orientations of the user's left and right eyes. A point ofconvergence may be the point where the two foveal axes of the user'seyes intersect. The direction of the user's gaze may be the direction ofa line passing through the point of convergence and the mid-pointbetween the pupils of the user's eyes.

Input/output interface 140 may be a device that allows a user to sendaction requests to console 110. An action request may be a request toperform a particular action. For example, an action request may be tostart or to end an application or to perform a particular action withinthe application. Input/output interface 140 may include one or moreinput devices. Example input devices may include a keyboard, a mouse, agame controller, a glove, a button, a touch screen, or any othersuitable device for receiving action requests and communicating thereceived action requests to console 110. An action request received bythe input/output interface 140 may be communicated to console 110, whichmay perform an action corresponding to the requested action. In someembodiments, input/output interface 140 may provide haptic feedback tothe user in accordance with instructions received from console 110. Forexample, input/output interface 140 may provide haptic feedback when anaction request is received, or when console 110 has performed arequested action and communicates instructions to input/output interface140. In some embodiments, external imaging device 150 may be used totrack input/output interface 140, such as tracking the location orposition of a controller (which may include, for example, an IR lightsource) or a hand of the user to determine the motion of the user. Insome embodiments, near-eye display 120 may include one or more imagingdevices to track input/output interface 140, such as tracking thelocation or position of a controller or a hand of the user to determinethe motion of the user.

Console 110 may provide content to near-eye display 120 for presentationto the user in accordance with information received from one or more ofexternal imaging device 150, near-eye display 120, and input/outputinterface 140. In the example shown in FIG. 1, console 110 may includean application store 112, a headset tracking module 114, an artificialreality engine 116, and an eye-tracking module 118. Some embodiments ofconsole 110 may include different or additional modules than thosedescribed in conjunction with FIG. 1. Functions further described belowmay be distributed among components of console 110 in a different mannerthan is described here.

In some embodiments, console 110 may include a processor and anon-transitory computer-readable storage medium storing instructionsexecutable by the processor. The processor may include multipleprocessing units executing instructions in parallel. The non-transitorycomputer-readable storage medium may be any memory, such as a hard diskdrive, a removable memory, or a solid-state drive (e.g., flash memory ordynamic random access memory (DRAM)). In various embodiments, themodules of console 110 described in conjunction with FIG. 1 may beencoded as instructions in the non-transitory computer-readable storagemedium that, when executed by the processor, cause the processor toperform the functions further described below.

Application store 112 may store one or more applications for executionby console 110. An application may include a group of instructions that,when executed by a processor, generates content for presentation to theuser. Content generated by an application may be in response to inputsreceived from the user via movement of the user's eyes or inputsreceived from the input/output interface 140. Examples of theapplications may include gaming applications, conferencing applications,video playback application, or other suitable applications.

Headset tracking module 114 may track movements of near-eye display 120using slow calibration information from external imaging device 150. Forexample, headset tracking module 114 may determine positions of areference point of near-eye display 120 using observed locators from theslow calibration information and a model of near-eye display 120.Headset tracking module 114 may also determine positions of a referencepoint of near-eye display 120 using position information from the fastcalibration information. Additionally, in some embodiments, headsettracking module 114 may use portions of the fast calibrationinformation, the slow calibration information, or any combinationthereof, to predict a future location of near-eye display 120. Headsettracking module 114 may provide the estimated or predicted futureposition of near-eye display 120 to artificial reality engine 116.

Artificial reality engine 116 may execute applications within artificialreality system environment 100 and receive position information ofnear-eye display 120, acceleration information of near-eye display 120,velocity information of near-eye display 120, predicted future positionsof near-eye display 120, or any combination thereof from headsettracking module 114. Artificial reality engine 116 may also receiveestimated eye position and orientation information from eye-trackingmodule 118. Based on the received information, artificial reality engine116 may determine content to provide to near-eye display 120 forpresentation to the user. For example, if the received informationindicates that the user has looked to the left, artificial realityengine 116 may generate content for near-eye display 120 that mirrorsthe user's eye movement in a virtual environment. Additionally,artificial reality engine 116 may perform an action within anapplication executing on console 110 in response to an action requestreceived from input/output interface 140, and provide feedback to theuser indicating that the action has been performed. The feedback may bevisual or audible feedback via near-eye display 120 or haptic feedbackvia input/output interface 140.

Eye-tracking module 118 may receive eye-tracking data from eye-trackingunit 130 and determine the position of the user's eye based on the eyetracking data. The position of the eye may include an eye's orientation,location, or both relative to near-eye display 120 or any elementthereof. Because the eye's axes of rotation change as a function of theeye's location in its socket, determining the eye's location in itssocket may allow eye-tracking module 118 to more accurately determinethe eye's orientation.

FIG. 2 is a perspective view of an example of a near-eye display in theform of an HMD device 200 for implementing some of the examplesdisclosed herein. HMD device 200 may be a part of, e.g., a VR system, anAR system, an MR system, or any combination thereof. HMD device 200 mayinclude a body 220 and a head strap 230. FIG. 2 shows a bottom side 223,a front side 225, and a left side 227 of body 220 in the perspectiveview. Head strap 230 may have an adjustable or extendible length. Theremay be a sufficient space between body 220 and head strap 230 of HMDdevice 200 for allowing a user to mount HMD device 200 onto the user'shead. In various embodiments, HMD device 200 may include additional,fewer, or different components. For example, in some embodiments, HMDdevice 200 may include eyeglass temples and temple tips as shown in, forexample, FIG. 3 below, rather than head strap 230.

HMD device 200 may present to a user media including virtual and/oraugmented views of a physical, real-world environment withcomputer-generated elements. Examples of the media presented by HMDdevice 200 may include images (e.g., two-dimensional (2D) orthree-dimensional (3D) images), videos (e.g., 2D or 3D videos), audio,or any combination thereof. The images and videos may be presented toeach eye of the user by one or more display assemblies (not shown inFIG. 2) enclosed in body 220 of HMD device 200. In various embodiments,the one or more display assemblies may include a single electronicdisplay panel or multiple electronic display panels (e.g., one displaypanel for each eye of the user). Examples of the electronic displaypanel(s) may include, for example, an LCD, an OLED display, an ILEDdisplay, a μLED display, an AMOLED, a TOLED, some other display, or anycombination thereof. HMD device 200 may include two eye box regions.

In some implementations, HMD device 200 may include various sensors (notshown), such as depth sensors, motion sensors, position sensors, and eyetracking sensors. Some of these sensors may use a structured lightpattern for sensing. In some implementations, HMD device 200 may includean input/output interface for communicating with a console. In someimplementations, HMD device 200 may include a virtual reality engine(not shown) that can execute applications within HMD device 200 andreceive depth information, position information, accelerationinformation, velocity information, predicted future positions, or anycombination thereof of HMD device 200 from the various sensors. In someimplementations, the information received by the virtual reality enginemay be used for producing a signal (e.g., display instructions) to theone or more display assemblies. In some implementations, HMD device 200may include locators (not shown, such as locators 126) located in fixedpositions on body 220 relative to one another and relative to areference point. Each of the locators may emit light that is detectableby an external imaging device.

FIG. 3 is a perspective view of an example of a near-eye display 300 inthe form of a pair of glasses for implementing some of the examplesdisclosed herein. Near-eye display 300 may be a specific implementationof near-eye display 120 of FIG. 1, and may be configured to operate as avirtual reality display, an augmented reality display, and/or a mixedreality display.

Near-eye display 300 may include a frame 305 and a display 310. Display310 may be configured to present content to a user. In some embodiments,display 310 may include display electronics and/or display optics. Forexample, as described above with respect to near-eye display 120 of FIG.1, display 310 may include an LCD display panel, an LED display panel,or an optical display panel (e.g., a waveguide display assembly).

Near-eye display 300 may further include various sensors 350 a , 350 b ,350 c , 350d, and 350 e on or within frame 305. In some embodiments,sensors 350 a -350 e may include one or more depth sensors, motionsensors, position sensors, inertial sensors, or ambient light sensors.In some embodiments, sensors 350 a -350 e may include one or more imagesensors configured to generate image data representing different fieldsof views in different directions. In some embodiments, sensors 350 a-350 e may be used as input devices to control or influence thedisplayed content of near-eye display 300, and/or to provide aninteractive VR/AR/MR experience to a user of near-eye display 300. Insome embodiments, sensors 350 a -350 e may also be used for stereoscopicimaging.

In some embodiments, near-eye display 300 may further include one ormore illuminators 330 to project light into the physical environment.The projected light may be associated with different frequency bands(e.g., visible light, infra-red light, ultra-violet light, etc.), andmay serve various purposes. For example, illuminator(s) 330 may projectlight in a dark environment (or in an environment with low intensity ofinfra-red light, ultra-violet light, etc.) to assist sensors 350 a -350e in capturing images of different objects within the dark environment.In some embodiments, illuminator(s) 330 may be used to project certainlight patterns onto the objects within the environment. In someembodiments, illuminator(s) 330 may be used as locators, such aslocators 126 described above with respect to FIG. 1.

In some embodiments, near-eye display 300 may also include ahigh-resolution camera 340. Camera 340 may capture images of thephysical environment in the field of view. The captured images may beprocessed, for example, by a virtual reality engine (e.g., artificialreality engine 116 of FIG. 1) to add virtual objects to the capturedimages or modify physical objects in the captured images, and theprocessed images may be displayed to the user by display 310 for AR orMR applications.

FIG. 4 illustrates an example of an optical see-through augmentedreality system 400 including a waveguide display according to certainembodiments. Augmented reality system 400 may include a projector 410and a combiner 415. Projector 410 may include a light source or imagesource 412 and projector optics 414. In some embodiments, light sourceor image source 412 may include one or more micro-LED devices describedabove. In some embodiments, image source 412 may include a plurality ofpixels that displays virtual objects, such as an LCD display panel or anLED display panel. In some embodiments, image source 412 may include alight source that generates coherent or partially coherent light. Forexample, image source 412 may include a laser diode, a vertical cavitysurface emitting laser, an LED, and/or a micro-LED described above. Insome embodiments, image source 412 may include a plurality of lightsources (e.g., an array of micro-LEDs described above), each emitting amonochromatic image light corresponding to a primary color (e.g., red,green, or blue). In some embodiments, image source 412 may include threetwo-dimensional arrays of micro-LEDs, where each two-dimensional arrayof micro-LEDs may include micro-LEDs configured to emit light of aprimary color (e.g., red, green, or blue). In some embodiments, imagesource 412 may include an optical pattern generator, such as a spatiallight modulator. Projector optics 414 may include one or more opticalcomponents that can condition the light from image source 412, such asexpanding, collimating, scanning, or projecting light from image source412 to combiner 415. The one or more optical components may include, forexample, one or more lenses, liquid lenses, mirrors, apertures, and/orgratings. For example, in some embodiments, image source 412 may includeone or more one-dimensional arrays or elongated two-dimensional arraysof micro-LEDs, and projector optics 414 may include one or moreone-dimensional scanners (e.g., micro-mirrors or prisms) configured toscan the one-dimensional arrays or elongated two-dimensional arrays ofmicro-LEDs to generate image frames. In some embodiments, projectoroptics 414 may include a liquid lens (e.g., a liquid crystal lens) witha plurality of electrodes that allows scanning of the light from imagesource 412.

Combiner 415 may include an input coupler 430 for coupling light fromprojector 410 into a substrate 420 of combiner 415. Combiner 415 maytransmit at least 50% of light in a first wavelength range and reflectat least 25% of light in a second wavelength range. For example, thefirst wavelength range may be visible light from about 400 nm to about650 nm, and the second wavelength range may be in the infrared band, forexample, from about 800 nm to about 1000 nm. Input coupler 430 mayinclude a volume holographic grating, a diffractive optical element(DOE) (e.g., a surface-relief grating), a slanted surface of substrate420, or a refractive coupler (e.g., a wedge or a prism). For example,input coupler 430 may include a reflective volume Bragg grating or atransmissive volume Bragg grating. Input coupler 430 may have a couplingefficiency of greater than 30%, 50%, 75%, 90%, or higher for visiblelight. Light coupled into substrate 420 may propagate within substrate420 through, for example, total internal reflection (TIR). Substrate 420may be in the form of a lens of a pair of eyeglasses.

Substrate 420 may have a flat or a curved surface, and may include oneor more types of dielectric materials, such as glass, quartz, plastic,polymer, poly(methyl methacrylate) (PMMA), crystal, or ceramic. Athickness of the substrate may range from, for example, less than about1 mm to about 10 mm or more. Substrate 420 may be transparent to visiblelight.

Substrate 420 may include or may be coupled to a plurality of outputcouplers 440, each configured to extract at least a portion of the lightguided by and propagating within substrate 420 from substrate 420, anddirect extracted light 460 to an eyebox 495 where an eye 490 of the userof augmented reality system 400 may be located when augmented realitysystem 400 is in use. The plurality of output couplers 440 may replicatethe exit pupil to increase the size of eyebox 495 such that thedisplayed image is visible in a larger area. As input coupler 430,output couplers 440 may include grating couplers (e.g., volumeholographic gratings or surface-relief gratings), other diffractionoptical elements (DOEs), prisms, etc. For example, output couplers 440may include reflective volume Bragg gratings or transmissive volumeBragg gratings. Output couplers 440 may have different coupling (e.g.,diffraction) efficiencies at different locations. Substrate 420 may alsoallow light 450 from the environment in front of combiner 415 to passthrough with little or no loss. Output couplers 440 may also allow light450 to pass through with little loss. For example, in someimplementations, output couplers 440 may have a very low diffractionefficiency for light 450 such that light 450 may be refracted orotherwise pass through output couplers 440 with little loss, and thusmay have a higher intensity than extracted light 460. In someimplementations, output couplers 440 may have a high diffractionefficiency for light 450 and may diffract light 450 in certain desireddirections (i.e., diffraction angles) with little loss. As a result, theuser may be able to view combined images of the environment in front ofcombiner 415 and images of virtual objects projected by projector 410.

FIG. 5A illustrates an example of a near-eye display (NED) device 500including a waveguide display 530 according to certain embodiments. NEDdevice 500 may be an example of near-eye display 120, augmented realitysystem 400, or another type of display device. NED device 500 mayinclude a light source 510, projection optics 520, and waveguide display530. Light source 510 may include multiple panels of light emitters fordifferent colors, such as a panel of red light emitters 512, a panel ofgreen light emitters 514, and a panel of blue light emitters 516. Thered light emitters 512 are organized into an array; the green lightemitters 514 are organized into an array; and the blue light emitters516 are organized into an array. The dimensions and pitches of lightemitters in light source 510 may be small. For example, each lightemitter may have a diameter less than 2 μm (e.g., about 1.2 μm) and thepitch may be less than 2 μm (e.g., about 1.5 μm). As such, the number oflight emitters in each red light emitters 512, green light emitters 514,and blue light emitters 516 can be equal to or greater than the numberof pixels in a display image, such as 960×720, 1280×720, 1440×1080,1920×1080, 2160×1080, or 2560×1080 pixels. Thus, a display image may begenerated simultaneously by light source 510. A scanning element may notbe used in NED device 500.

Before reaching waveguide display 530, the light emitted by light source510 may be conditioned by projection optics 520, which may include alens array. Projection optics 520 may collimate or focus the lightemitted by light source 510 to waveguide display 530, which may includea coupler 532 for coupling the light emitted by light source 510 intowaveguide display 530. The light coupled into waveguide display 530 maypropagate within waveguide display 530 through, for example, totalinternal reflection as described above with respect to FIG. 4. Coupler532 may also couple portions of the light propagating within waveguidedisplay 530 out of waveguide display 530 and towards user's eye 590.

FIG. 5B illustrates an example of a near-eye display (NED) device 550including a waveguide display 580 according to certain embodiments. Insome embodiments, NED device 550 may use a scanning mirror 570 toproject light from a light source 540 to an image field where a user'seye 590 may be located. NED device 550 may be an example of near-eyedisplay 120, augmented reality system 400, or another type of displaydevice. Light source 540 may include one or more rows or one or morecolumns of light emitters of different colors, such as multiple rows ofred light emitters 542, multiple rows of green light emitters 544, andmultiple rows of blue light emitters 546. For example, red lightemitters 542, green light emitters 544, and blue light emitters 546 mayeach include N rows, each row including, for example, 2560 lightemitters (pixels). The red light emitters 542 are organized into anarray; the green light emitters 544 are organized into an array; and theblue light emitters 546 are organized into an array. In someembodiments, light source 540 may include a single line of lightemitters for each color. In some embodiments, light source 540 mayinclude multiple columns of light emitters for each of red, green, andblue colors, where each column may include, for example, 1080 lightemitters. In some embodiments, the dimensions and/or pitches of thelight emitters in light source 540 may be relatively large (e.g., about3-5 μm) and thus light source 540 may not include sufficient lightemitters for simultaneously generating a full display image. Forexample, the number of light emitters for a single color may be fewerthan the number of pixels (e.g., 2560×1080 pixels) in a display image.The light emitted by light source 540 may be a set of collimated ordiverging beams of light.

Before reaching scanning mirror 570, the light emitted by light source540 may be conditioned by various optical devices, such as collimatinglenses or a freeform optical element 560. Freeform optical element 560may include, for example, a multi-facet prism or another light foldingelement that may direct the light emitted by light source 540 towardsscanning mirror 570, such as changing the propagation direction of thelight emitted by light source 540 by, for example, about 90° or larger.In some embodiments, freeform optical element 560 may be rotatable toscan the light. Scanning mirror 570 and/or freeform optical element 560may reflect and project the light emitted by light source 540 towaveguide display 580, which may include a coupler 582 for coupling thelight emitted by light source 540 into waveguide display 580. The lightcoupled into waveguide display 580 may propagate within waveguidedisplay 580 through, for example, total internal reflection as describedabove with respect to FIG. 4. Coupler 582 may also couple portions ofthe light propagating within waveguide display 580 out of waveguidedisplay 580 and towards user's eye 590.

Scanning mirror 570 may include a microelectromechanical system (MEMS)mirror or any other suitable mirrors. Scanning mirror 570 may rotate toscan in one or two dimensions. As scanning mirror 570 rotates, the lightemitted by light source 540 may be directed to a different area ofwaveguide display 580 such that a full display image may be projectedonto waveguide display 580 and directed to user's eye 590 by waveguidedisplay 580 in each scanning cycle. For example, in embodiments wherelight source 540 includes light emitters for all pixels in one or morerows or columns, scanning mirror 570 may be rotated in the column or rowdirection (e.g., x or y direction) to scan an image. In embodimentswhere light source 540 includes light emitters for some but not allpixels in one or more rows or columns, scanning mirror 570 may berotated in both the row and column directions (e.g., both x and ydirections) to project a display image (e.g., using a raster-typescanning pattern).

NED device 550 may operate in predefined display periods. A displayperiod (e.g., display cycle) may refer to a duration of time in which afull image is scanned or projected. For example, a display period may bea reciprocal of the desired frame rate. In NED device 550 that includesscanning mirror 570, the display period may also be referred to as ascanning period or scanning cycle. The light generation by light source540 may be synchronized with the rotation of scanning mirror 570. Forexample, each scanning cycle may include multiple scanning steps, wherelight source 540 may generate a different light pattern in eachrespective scanning step.

In each scanning cycle, as scanning mirror 570 rotates, a display imagemay be projected onto waveguide display 580 and user's eye 590. Theactual color value and light intensity (e.g., brightness) of a givenpixel location of the display image may be an average of the light beamsof the three colors (e.g., red, green, and blue) illuminating the pixellocation during the scanning period. After completing a scanning period,scanning mirror 570 may revert back to the initial position to projectlight for the first few rows of the next display image or may rotate ina reverse direction or scan pattern to project light for the nextdisplay image, where a new set of driving signals may be fed to lightsource 540. The same process may be repeated as scanning mirror 570rotates in each scanning cycle. As such, different images may beprojected to user's eye 590 in different scanning cycles.

FIG. 6 illustrates an example of an image source assembly 610 in anear-eye display system 600 according to certain embodiments. Imagesource assembly 610 may include, for example, a display panel 640 thatmay generate display images to be projected to the user's eyes, and aprojector 650 that may project the display images generated by displaypanel 640 to a waveguide display as described above with respect toFIGS. 4-5B. Display panel 640 may include a light source 642 and adriver circuit 644 for light source 642. Light source 642 may include,for example, light source 510 or 540. Projector 650 may include, forexample, freeform optical element 560, scanning mirror 570, and/orprojection optics 520 described above. Near-eye display system 600 mayalso include a controller 620 that synchronously controls light source642 and projector 650 (e.g., scanning mirror 570). Image source assembly610 may generate and output an image light to a waveguide display (notshown in FIG. 6), such as waveguide display 530 or 580. As describedabove, the waveguide display may receive the image light at one or moreinput-coupling elements, and guide the received image light to one ormore output-coupling elements. The input and output coupling elementsmay include, for example, a diffraction grating, a holographic grating,a prism, or any combination thereof. The input-coupling element may bechosen such that total internal reflection occurs with the waveguidedisplay. The output-coupling element may couple portions of the totalinternally reflected image light out of the waveguide display.

As described above, light source 642 may include a plurality of lightemitters arranged in an array or a matrix. Each light emitter may emitmonochromatic light, such as red light, blue light, green light,infra-red light, and the like. While RGB colors are often discussed inthis disclosure, embodiments described herein are not limited to usingred, green, and blue as primary colors. Other colors can also be used asthe primary colors of near-eye display system 600. In some embodiments,a display panel in accordance with an embodiment may use more than threeprimary colors. Each pixel in light source 642 may include threesubpixels that include a red micro-LED, a green micro-LED, and a bluemicro-LED. A semiconductor LED generally includes an active lightemitting layer within multiple layers of semiconductor materials. Themultiple layers of semiconductor materials may include differentcompound materials or a same base material with different dopants and/ordifferent doping densities. For example, the multiple layers ofsemiconductor materials may include an n-type material layer, an activeregion that may include hetero-structures (e.g., one or more quantumwells), and a p-type material layer. The multiple layers ofsemiconductor materials may be grown on a surface of a substrate havinga certain orientation. In some embodiments, to increase light extractionefficiency, a mesa that includes at least some of the layers ofsemiconductor materials may be formed.

Controller 620 may control the image rendering operations of imagesource assembly 610, such as the operations of light source 642 and/orprojector 650. For example, controller 620 may determine instructionsfor image source assembly 610 to render one or more display images. Theinstructions may include display instructions and scanning instructions.In some embodiments, the display instructions may include an image file(e.g., a bitmap file). The display instructions may be received from,for example, a console, such as console 110 described above with respectto FIG. 1. The scanning instructions may be used by image sourceassembly 610 to generate image light. The scanning instructions mayspecify, for example, a type of a source of image light (e.g.,monochromatic or polychromatic), a scanning rate, an orientation of ascanning apparatus, one or more illumination parameters, or anycombination thereof. Controller 620 may include a combination ofhardware, software, and/or firmware not shown here so as not to obscureother aspects of the present disclosure.

In some embodiments, controller 620 may be a graphics processing unit(GPU) of a display device. In other embodiments, controller 620 may beother kinds of processors. The operations performed by controller 620may include taking content for display and dividing the content intodiscrete sections. Controller 620 may provide to light source 642scanning instructions that include an address corresponding to anindividual source element of light source 642 and/or an electrical biasapplied to the individual source element. Controller 620 may instructlight source 642 to sequentially present the discrete sections usinglight emitters corresponding to one or more rows of pixels in an imageultimately displayed to the user. Controller 620 may also instructprojector 650 to perform different adjustments of the light. Forexample, controller 620 may control projector 650 to scan the discretesections to different areas of a coupling element of the waveguidedisplay (e.g., waveguide display 580) as described above with respect toFIG. 5B. As such, at the exit pupil of the waveguide display, eachdiscrete portion is presented in a different respective location. Whileeach discrete section is presented at a different respective time, thepresentation and scanning of the discrete sections occur fast enoughsuch that a user's eye may integrate the different sections into asingle image or series of images.

Image processor 630 may be a general-purpose processor and/or one ormore application-specific circuits that are dedicated to performing thefeatures described herein. In one embodiment, a general-purposeprocessor may be coupled to a memory to execute software instructionsthat cause the processor to perform certain processes described herein.In another embodiment, image processor 630 may be one or more circuitsthat are dedicated to performing certain features. While image processor630 in FIG. 6 is shown as a stand-alone unit that is separate fromcontroller 620 and driver circuit 644, image processor 630 may be asub-unit of controller 620 or driver circuit 644 in other embodiments.In other words, in those embodiments, controller 620 or driver circuit644 may perform various image processing functions of image processor630. Image processor 630 may also be referred to as an image processingcircuit.

In the example shown in FIG. 6, light source 642 may be driven by drivercircuit 644, based on data or instructions (e.g., display and scanninginstructions) sent from controller 620 or image processor 630. In oneembodiment, driver circuit 644 may include a circuit panel that connectsto and mechanically holds various light emitters of light source 642.Light source 642 may emit light in accordance with one or moreillumination parameters that are set by the controller 620 andpotentially adjusted by image processor 630 and driver circuit 644. Anillumination parameter may be used by light source 642 to generatelight. An illumination parameter may include, for example, sourcewavelength, pulse rate, pulse amplitude, beam type (continuous orpulsed), other parameter(s) that may affect the emitted light, or anycombination thereof. In some embodiments, the source light generated bylight source 642 may include multiple beams of red light, green light,and blue light, or any combination thereof

Projector 650 may perform a set of optical functions, such as focusing,combining, conditioning, or scanning the image light generated by lightsource 642. In some embodiments, projector 650 may include a combiningassembly, a light conditioning assembly, or a scanning mirror assembly.Projector 650 may include one or more optical components that opticallyadjust and potentially re-direct the light from light source 642. Oneexample of the adjustment of light may include conditioning the light,such as expanding, collimating, correcting for one or more opticalerrors (e.g., field curvature, chromatic aberration, etc.), some otheradjustments of the light, or any combination thereof. The opticalcomponents of projector 650 may include, for example, lenses, mirrors,apertures, gratings, or any combination thereof

Projector 650 may redirect image light via its one or more reflectiveand/or refractive portions so that the image light is projected atcertain orientations toward the waveguide display. The location wherethe image light is redirected toward the waveguide display may depend onspecific orientations of the one or more reflective and/or refractiveportions. In some embodiments, projector 650 includes a single scanningmirror that scans in at least two dimensions. In other embodiments,projector 650 may include a plurality of scanning mirrors that each scanin directions orthogonal to each other. Projector 650 may perform araster scan (horizontally or vertically), a bi-resonant scan, or anycombination thereof. In some embodiments, projector 650 may perform acontrolled vibration along the horizontal and/or vertical directionswith a specific frequency of oscillation to scan along two dimensionsand generate a two-dimensional projected image of the media presented touser's eyes. In other embodiments, projector 650 may include a lens orprism that may serve similar or the same function as one or morescanning mirrors. In some embodiments, image source assembly 610 may notinclude a projector, where the light emitted by light source 642 may bedirectly incident on the waveguide display.

In semiconductor LEDs, photons are usually generated at a certaininternal quantum efficiency through the recombination of electrons andholes within an active region (e.g., one or more semiconductor layers),where the internal quantum efficiency is the proportion of the radiativeelectron-hole recombination in the active region that emits photons. Thegenerated light may then be extracted from the LEDs in a particulardirection or within a particular solid angle. The ratio between thenumber of emitted photons extracted from an LED and the number ofelectrons passing through the LED is referred to as the external quantumefficiency, which describes how efficiently the LED converts injectedelectrons to photons that are extracted from the device.

The external quantum efficiency may be proportional to the injectionefficiency, the internal quantum efficiency, and the extractionefficiency. The injection efficiency refers to the proportion ofelectrons passing through the device that are injected into the activeregion. The extraction efficiency is the proportion of photons generatedin the active region that escape from the device. For LEDs, and inparticular, micro-LEDs with reduced physical dimensions, improving theinternal and external quantum efficiency and/or controlling the emissionspectrum may be challenging. In some embodiments, to increase the lightextraction efficiency, a mesa that includes at least some of the layersof semiconductor materials may be formed.

FIG. 7A illustrates an example of an LED 700 having a vertical mesastructure. LED 700 may be a light emitter in light source 510, 540, or642. LED 700 may be a micro-LED made of inorganic materials, such asmultiple layers of semiconductor materials. The layered semiconductorlight emitting device may include multiple layers of III-V semiconductormaterials. A III-V semiconductor material may include one or more GroupIII elements, such as aluminum (Al), gallium (Ga), or indium (In), incombination with a Group V element, such as nitrogen (N), phosphorus(P), arsenic (As), or antimony (Sb). When the Group V element of theIII-V semiconductor material includes nitrogen, the III-V semiconductormaterial is referred to as a III-nitride material. The layeredsemiconductor light emitting device may be manufactured by growingmultiple epitaxial layers on a substrate using techniques such asvapor-phase epitaxy (VPE), liquid-phase epitaxy (LPE), molecular beamepitaxy (MBE), or metalorganic chemical vapor deposition (MOCVD). Forexample, the layers of the semiconductor materials may be grownlayer-by-layer on a substrate with a certain crystal lattice orientation(e.g., polar, nonpolar, or semi-polar orientation), such as a GaN, GaAs,or GaP substrate, or a substrate including, but not limited to,sapphire, silicon carbide, silicon, zinc oxide, boron nitride, lithiumaluminate, lithium niobate, germanium, aluminum nitride, lithiumgallate, partially substituted spinels, or quaternary tetragonal oxidessharing the beta-LiAlO₂ structure, where the substrate may be cut in aspecific direction to expose a specific plane as the growth surface.

In the example shown in FIG. 7A, LED 700 may include a substrate 710,which may include, for example, a sapphire substrate or a GaN substrate.A semiconductor layer 720 may be grown on substrate 710. Semiconductorlayer 720 may include a III-V material, such as GaN, and may be p-doped(e.g., with Mg, Ca, Zn, or Be) or n-doped (e.g., with Si or Ge). One ormore active layers 730 may be grown on semiconductor layer 720 to forman active region. Active layer 730 may include III-V materials, such asone or more InGaN layers, one or more AlInGaP layers, and/or one or moreGaN layers, which may form one or more heterostructures, such as one ormore quantum wells or MQWs. A semiconductor layer 740 may be grown onactive layer 730. Semiconductor layer 740 may include a III-V material,such as GaN, and may be p-doped (e.g., with Mg, Ca, Zn, or Be) orn-doped (e.g., with Si or Ge). One of semiconductor layer 720 andsemiconductor layer 740 may be a p-type layer and the other one may bean n-type layer. Semiconductor layer 720 and semiconductor layer 740sandwich active layer 730 to form the light emitting region. Forexample, LED 700 may include a layer of InGaN situated between a layerof p-type GaN doped with magnesium and a layer of n-type GaN doped withsilicon or oxygen. In some embodiments, LED 700 may include a layer ofAlInGaP situated between a layer of p-type AlInGaP doped with zinc ormagnesium and a layer of n-type AlInGaP doped with selenium, silicon, ortellurium.

In some embodiments, an electron-blocking layer (EBL) (not shown in FIG.7A) may be grown to form a layer between active layer 730 and at leastone of semiconductor layer 720 or semiconductor layer 740. The EBL mayreduce the electron leakage current and improve the efficiency of theLED. In some embodiments, a heavily-doped semiconductor layer 750, suchas a P⁺ or P⁺⁺ semiconductor layer, may be formed on semiconductor layer740 and act as a contact layer for forming an ohmic contact and reducingthe contact impedance of the device. In some embodiments, a conductivelayer 760 may be formed on heavily-doped semiconductor layer 750.Conductive layer 760 may include, for example, an indium tin oxide (ITO)or Al/Ni/Au film. In one example, conductive layer 760 may include atransparent ITO layer.

To make contact with semiconductor layer 720 (e.g., an n-GaN layer) andto more efficiently extract light emitted by active layer 730 from LED700, the semiconductor material layers (including heavily-dopedsemiconductor layer 750, semiconductor layer 740, active layer 730, andsemiconductor layer 720) may be etched to expose semiconductor layer 720and to form a mesa structure that includes layers 720-760. The mesastructure may confine the carriers within the device. Etching the mesastructure may lead to the formation of mesa sidewalls 732 that may beorthogonal to the growth planes. A passivation layer 770 may be formedon sidewalls 732 of the mesa structure. Passivation layer 770 mayinclude an oxide layer, such as a SiO₂ layer, and may act as a reflectorto reflect emitted light out of LED 700. A contact layer 780, which mayinclude a metal layer, such as Al, Au, Ni, Ti, or any combinationthereof, may be formed on semiconductor layer 720 and may act as anelectrode of LED 700. In addition, another contact layer 790, such as anAl/Ni/Au metal layer, may be formed on conductive layer 760 and may actas another electrode of LED 700.

When a voltage signal is applied to contact layers 780 and 790,electrons and holes may recombine in active layer 730, where therecombination of electrons and holes may cause photon emission. Thewavelength and energy of the emitted photons may depend on the energybandgap between the valence band and the conduction band in active layer730. For example, InGaN active layers may emit green or blue light,AlGaN active layers may emit blue to ultraviolet light, while AlInGaPactive layers may emit red, orange, yellow, or green light. The emittedphotons may be reflected by passivation layer 770 and may exit LED 700from the top (e.g., conductive layer 760 and contact layer 790) orbottom (e.g., substrate 710).

In some embodiments, LED 700 may include one or more other components,such as a lens, on the light emission surface, such as substrate 710, tofocus or collimate the emitted light or couple the emitted light into awaveguide. In some embodiments, an LED may include a mesa of anothershape, such as planar, conical, semi-parabolic, or parabolic, and a basearea of the mesa may be circular, rectangular, hexagonal, or triangular.For example, the LED may include a mesa of a curved shape (e.g.,paraboloid shape) and/or a non-curved shape (e.g., conic shape). Themesa may be truncated or non-truncated.

FIG. 7B is a cross-sectional view of an example of an LED 705 having aparabolic mesa structure. Similar to LED 700, LED 705 may includemultiple layers of semiconductor materials, such as multiple layers ofIII-V semiconductor materials. The semiconductor material layers may beepitaxially grown on a substrate 715, such as a GaN substrate or asapphire substrate. For example, a semiconductor layer 725 may be grownon substrate 715. Semiconductor layer 725 may include a III-V material,such as GaN, and may be p-doped (e.g., with Mg, Ca, Zn, or Be) orn-doped (e.g., with Si or Ge). One or more active layer 735 may be grownon semiconductor layer 725. Active layer 735 may include III-Vmaterials, such as one or more InGaN layers, one or more AlInGaP layers,and/or one or more GaN layers, which may form one or moreheterostructures, such as one or more quantum wells. A semiconductorlayer 745 may be grown on active layer 735. Semiconductor layer 745 mayinclude a III-V material, such as GaN, and may be p-doped (e.g., withMg, Ca, Zn, or Be) or n-doped (e.g., with Si or Ge). One ofsemiconductor layer 725 and semiconductor layer 745 may be a p-typelayer and the other one may be an n-type layer.

To make contact with semiconductor layer 725 (e.g., an n-type GaN layer)and to more efficiently extract light emitted by active layer 735 fromLED 705, the semiconductor layers may be etched to expose semiconductorlayer 725 and to form a mesa structure that includes layers 725-745. Themesa structure may confine carriers within the injection area of thedevice. Etching the mesa structure may lead to the formation of mesaside walls (also referred to herein as facets) that may be non-parallelwith, or in some cases, orthogonal, to the growth planes associated withcrystalline growth of layers 725-745.

As shown in FIG. 7B, LED 705 may have a mesa structure that includes aflat top. A dielectric layer 775 (e.g., SiO₂ or SiNx) may be formed onthe facets of the mesa structure. In some embodiments, dielectric layer775 may include multiple layers of dielectric materials. In someembodiments, a metal layer 795 may be formed on dielectric layer 775.Metal layer 795 may include one or more metal or metal alloy materials,such as aluminum (Al), silver (Ag), gold (Au), platinum (Pt), titanium(Ti), copper (Cu), or any combination thereof. Dielectric layer 775 andmetal layer 795 may form a mesa reflector that can reflect light emittedby active layer 735 toward substrate 715. In some embodiments, the mesareflector may be parabolic-shaped to act as a parabolic reflector thatmay at least partially collimate the emitted light.

Electrical contact 765 and electrical contact 785 may be formed onsemiconductor layer 745 and semiconductor layer 725, respectively, toact as electrodes. Electrical contact 765 and electrical contact 785 mayeach include a conductive material, such as Al, Au, Pt, Ag, Ni, Ti, Cu,or any combination thereof (e.g., Ag/Pt/Au or Al/Ni/Au), and may act asthe electrodes of LED 705. In the example shown in FIG. 7B, electricalcontact 785 may be an n-contact, and electrical contact 765 may be ap-contact. Electrical contact 765 and semiconductor layer 745 (e.g., ap-type semiconductor layer) may form a back reflector for reflectinglight emitted by active layer 735 back toward substrate 715. In someembodiments, electrical contact 765 and metal layer 795 include samematerial(s) and can be formed using the same processes. In someembodiments, an additional conductive layer (not shown) may be includedas an intermediate conductive layer between the electrical contacts 765and 785 and the semiconductor layers.

When a voltage signal is applied across contacts 765 and 785, electronsand holes may recombine in active layer 735. The recombination ofelectrons and holes may cause photon emission, thus producing light. Thewavelength and energy of the emitted photons may depend on the energybandgap between the valence band and the conduction band in active layer735. For example, InGaN active layers may emit green or blue light,while AlInGaP active layers may emit red, orange, yellow, or greenlight. The emitted photons may propagate in many different directions,and may be reflected by the mesa reflector and/or the back reflector andmay exit LED 705, for example, from the bottom side (e.g., substrate715) shown in FIG. 7B. One or more other secondary optical components,such as a lens or a grating, may be formed on the light emissionsurface, such as substrate 715, to focus or collimate the emitted lightand/or couple the emitted light into a waveguide.

One or two-dimensional arrays of the LEDs described above may bemanufactured on a wafer to form light sources (e.g., light source 642).Driver circuits (e.g., driver circuit 644) may be fabricated, forexample, on a silicon wafer using CMOS processes. The LEDs and thedriver circuits on wafers may be diced and then bonded together, or maybe bonded on the wafer level and then diced. Various bonding techniquescan be used for bonding the LEDs and the driver circuits, such asadhesive bonding, metal-to-metal bonding, metal oxide bonding,wafer-to-wafer bonding, die-to-wafer bonding, hybrid bonding, and thelike.

FIG. 8A illustrates an example of a method of die-to-wafer bonding forarrays of LEDs according to certain embodiments. In the example shown inFIG. 8A, an LED array 801 may include a plurality of LEDs 807 on acarrier substrate 805. Carrier substrate 805 may include variousmaterials, such as GaAs, InP, GaN, AlN, sapphire, SiC, Si, or the like.LEDs 807 may be fabricated by, for example, growing various epitaxiallayers, forming mesa structures, and forming electrical contacts orelectrodes, before performing the bonding. The epitaxial layers mayinclude various materials, such as GaN, InGaN, (AlGaIn)P, (AlGaIn)AsP,(AlGaIn)AsN, (AlGaIn)Pas, (Eu:InGa)N, (AlGaIn)N, or the like, and mayinclude an n-type layer, a p-type layer, and an active layer thatincludes one or more heterostructures, such as one or more quantum wellsor MQWs. The electrical contacts may include various conductivematerials, such as a metal or a metal alloy.

A wafer 803 may include a base layer 809 having passive or activeintegrated circuits (e.g., driver circuits 811) fabricated thereon. Baselayer 809 may include, for example, a silicon wafer. Driver circuits 811may be used to control the operations of LEDs 807. For example, thedriver circuit for each LED 807 may include a 2T1C pixel structure thathas two transistors and one capacitor. Wafer 803 may also include abonding layer 813. Bonding layer 813 may include various materials, suchas a metal, an oxide, a dielectric, CuSn, AuTi, and the like. In someembodiments, a patterned layer 815 may be formed on a surface of bondinglayer 813, where patterned layer 815 may include a metallic grid made ofa conductive material, such as Cu, Ag, Au, Al, or the like.

LED array 801 may be bonded to wafer 803 via bonding layer 813 orpatterned layer 815. For example, patterned layer 815 may include metalpads or bumps made of various materials, such as CuSn, AuSn, ornanoporous Au, that may be used to align LEDs 807 of LED array 801 withcorresponding driver circuits 811 on wafer 803. In one example, LEDarray 801 may be brought toward wafer 803 until LEDs 807 come intocontact with respective metal pads or bumps corresponding to drivercircuits 811. Some or all of LEDs 807 may be aligned with drivercircuits 811, and may then be bonded to wafer 803 via patterned layer815 by various bonding techniques, such as metal-to-metal bonding. AfterLEDs 807 have been bonded to wafer 803, carrier substrate 805 may beremoved from LEDs 807.

FIG. 8B illustrates an example of a method of wafer-to-wafer bonding forarrays of LEDs according to certain embodiments. As shown in FIG. 8B, afirst wafer 802 may include a substrate 804, a first semiconductor layer806, active layers 808, and a second semiconductor layer 810. Substrate804 may include various materials, such as GaAs, InP, GaN, A1N,sapphire, SiC, Si, or the like. First semiconductor layer 806, activelayers 808, and second semiconductor layer 810 may include varioussemiconductor materials, such as GaN, InGaN, (AlGaIn)P, (AlGaIn)AsP,(AlGaIn)AsN, (AlGaIn)Pas, (Eu:InGa)N, (AlGaIn)N, or the like. In someembodiments, first semiconductor layer 806 may be an n-type layer, andsecond semiconductor layer 810 may be a p-type layer. For example, firstsemiconductor layer 806 may be an n-doped GaN layer (e.g., doped with Sior Ge), and second semiconductor layer 810 may be a p-doped GaN layer(e.g., doped with Mg, Ca, Zn, or Be). Active layers 808 may include, forexample, one or more GaN layers, one or more InGaN layers, one or moreAlInGaP layers, and the like, which may form one or moreheterostructures, such as one or more quantum wells or MQWs.

In some embodiments, first wafer 802 may also include a bonding layer.Bonding layer 812 may include various materials, such as a metal, anoxide, a dielectric, CuSn, AuTi, or the like. In one example, bondinglayer 812 may include p-contacts and/or n-contacts (not shown). In someembodiments, other layers may also be included on first wafer 802, suchas a buffer layer between substrate 804 and first semiconductor layer806. The buffer layer may include various materials, such aspolycrystalline GaN or A1N. In some embodiments, a contact layer may bebetween second semiconductor layer 810 and bonding layer 812. Thecontact layer may include any suitable material for providing anelectrical contact to second semiconductor layer 810 and/or firstsemiconductor layer 806.

First wafer 802 may be bonded to wafer 803 that includes driver circuits811 and bonding layer 813 as described above, via bonding layer 813and/or bonding layer 812. Bonding layer 812 and bonding layer 813 may bemade of the same material or different materials. Bonding layer 813 andbonding layer 812 may be substantially flat. First wafer 802 may bebonded to wafer 803 by various methods, such as metal-to-metal bonding,eutectic bonding, metal oxide bonding, anodic bonding,thermo-compression bonding, ultraviolet (UV) bonding, and/or fusionbonding.

As shown in FIG. 8B, first wafer 802 may be bonded to wafer 803 with thep-side (e.g., second semiconductor layer 810) of first wafer 802 facingdown (i.e., toward wafer 803). After bonding, substrate 804 may beremoved from first wafer 802, and first wafer 802 may then be processedfrom the n-side. The processing may include, for example, the formationof certain mesa shapes for individual LEDs, as well as the formation ofoptical components corresponding to the individual LEDs.

FIGS. 9A-9D illustrate an example of a method of hybrid bonding forarrays of LEDs according to certain embodiments. The hybrid bonding maygenerally include wafer cleaning and activation, high-precisionalignment of contacts of one wafer with contacts of another wafer,dielectric bonding of dielectric materials at the surfaces of the wafersat room temperature, and metal bonding of the contacts by annealing atelevated temperatures. FIG. 9A shows a substrate 910 with passive oractive circuits 920 manufactured thereon. As described above withrespect to FIGS. 8A-8B, substrate 910 may include, for example, asilicon wafer. Circuits 920 may include driver circuits for the arraysof LEDs. A bonding layer may include dielectric regions 940 and contactpads 930 connected to circuits 920 through electrical interconnects 922.Contact pads 930 may include, for example, Cu, Ag, Au, Al, W, Mo, Ni,Ti, Pt, Pd, or the like. Dielectric materials in dielectric regions 940may include SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. Thebonding layer may be planarized and polished using, for example,chemical mechanical polishing, where the planarization or polishing maycause dishing (a bowl like profile) in the contact pads. The surfaces ofthe bonding layers may be cleaned and activated by, for example, an ion(e.g., plasma) or fast atom (e.g., Ar) beam 905. The activated surfacemay be atomically clean and may be reactive for formation of directbonds between wafers when they are brought into contact, for example, atroom temperature.

FIG. 9B illustrates a wafer 950 including an array of micro-LEDs 970fabricated thereon as described above with respect to, for example,FIGS. 7A-8B. Wafer 950 may be a carrier wafer and may include, forexample, GaAs, InP, GaN, A1N, sapphire, SiC, Si, or the like. Micro-LEDs970 may include an n-type layer, an active region, and a p-type layerepitaxially grown on wafer 950. The epitaxial layers may include variousIII-V semiconductor materials described above, and may be processed fromthe p-type layer side to etch mesa structures in the epitaxial layers,such as substantially vertical structures, parabolic structures, conicstructures, or the like. Passivation layers and/or reflection layers maybe formed on the sidewalls of the mesa structures. P-contacts 980 andn-contacts 982 may be formed in a dielectric material layer 960deposited on the mesa structures and may make electrical contacts withthe p-type layer and the n-type layers, respectively. Dielectricmaterials in dielectric material layer 960 may include, for example,SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. P-contacts 980and n-contacts 982 may include, for example, Cu, Ag, Au, Al, W, Mo, Ni,Ti, Pt, Pd, or the like. The top surfaces of p-contacts 980, n-contacts982, and dielectric material layer 960 may form a bonding layer. Thebonding layer may be planarized and polished using, for example,chemical mechanical polishing, where the polishing may cause dishing inp-contacts 980 and n-contacts 982. The bonding layer may then be cleanedand activated by, for example, an ion (e.g., plasma) or fast atom (e.g.,Ar) beam 915. The activated surface may be atomically clean and reactivefor formation of direct bonds between wafers when they are brought intocontact, for example, at room temperature.

FIG. 9C illustrates a room temperature bonding process for bonding thedielectric materials in the bonding layers. For example, after thebonding layer that includes dielectric regions 940 and contact pads 930and the bonding layer that includes p-contacts 980, n-contacts 982, anddielectric material layer 960 are surface activated, wafer 950 andmicro-LEDs 970 may be turned upside down and brought into contact withsubstrate 910 and the circuits formed thereon. In some embodiments,compression pressure 925 may be applied to substrate 910 and wafer 950such that the bonding layers are pressed against each other. Due to thesurface activation and the dishing in the contacts, dielectric regions940 and dielectric material layer 960 may be in direct contact becauseof the surface attractive force, and may react and form chemical bondsbetween them because the surface atoms may have dangling bonds and maybe in unstable energy states after the activation. Thus, the dielectricmaterials in dielectric regions 940 and dielectric material layer 960may be bonded together with or without heat treatment or pressure.

FIG. 9D illustrates an annealing process for bonding the contacts in thebonding layers after bonding the dielectric materials in the bondinglayers. For example, contact pads 930 and p-contacts 980 or n-contacts982 may be bonded together by annealing at, for example, about 200-400°C. or higher. During the annealing process, heat 935 may cause thecontacts to expand more than the dielectric materials (due to differentcoefficients of thermal expansion), and thus may close the dishing gapsbetween the contacts such that contact pads 930 and p-contacts 980 orn-contacts 982 may be in contact and may form direct metallic bonds atthe activated surfaces.

In some embodiments where the two bonded wafers include materials havingdifferent coefficients of thermal expansion (CTEs), the dielectricmaterials bonded at room temperature may help to reduce or preventmisalignment of the contact pads caused by the different thermalexpansions. In some embodiments, to further reduce or avoid themisalignment of the contact pads at a high temperature during annealing,trenches may be formed between micro-LEDs, between groups of micro-LEDs,through part or all of the substrate, or the like, before bonding.

After the micro-LEDs are bonded to the driver circuits, the substrate onwhich the micro-LEDs are fabricated may be thinned or removed, andvarious secondary optical components may be fabricated on the lightemitting surfaces of the micro-LEDs to, for example, extract, collimate,and redirect the light emitted from the active regions of themicro-LEDs. In one example, micro-lenses may be formed on themicro-LEDs, where each micro-lens may correspond to a respectivemicro-LED and may help to improve the light extraction efficiency andcollimate the light emitted by the micro-LED. In some embodiments, thesecondary optical components may be fabricated in the substrate or then-type layer of the micro-LEDs. In some embodiments, the secondaryoptical components may be fabricated in a dielectric layer deposited onthe n-type side of the micro-LEDs. Examples of the secondary opticalcomponents may include a lens, a grating, an antireflection (AR)coating, a prism, a photonic crystal, or the like.

FIG. 10 illustrates an example of an LED array 1000 with secondaryoptical components fabricated thereon according to certain embodiments.LED array 1000 may be made by bonding an LED chip or wafer with asilicon wafer including electrical circuits fabricated thereon, usingany suitable bonding techniques described above with respect to, forexample, FIGS. 8A-9D. In the example shown in FIG. 10, LED array 1000may be bonded using a wafer-to-wafer hybrid bonding technique asdescribed above with respect to FIG. 9A-9D. LED array 1000 may include asubstrate 1010, which may be, for example, a silicon wafer. Integratedcircuits 1020, such as LED driver circuits, may be fabricated onsubstrate 1010. Integrated circuits 1020 may be connected to p-contacts1074 and n-contacts 1072 of micro-LEDs 1070 through interconnects 1022and contact pads 1030, where contact pads 1030 may form metallic bondswith p-contacts 1074 and n-contacts 1072. Dielectric layer 1040 onsubstrate 1010 may be bonded to dielectric layer 1060 through fusionbonding.

The substrate (not shown) of the LED chip or wafer may be thinned or maybe removed to expose the n-type layer 1050 of micro-LEDs 1070. Varioussecondary optical components, such as a spherical micro-lens 1082, agrating 1084, a micro-lens 1086, an antireflection layer 1088, and thelike, may be formed in or on top of n-type layer 1050. For example,spherical micro-lens arrays may be etched in the semiconductor materialsof micro-LEDs 1070 using a gray-scale mask and a photoresist with alinear response to exposure light, or using an etch mask formed bythermal reflowing of a patterned photoresist layer. The secondaryoptical components may also be etched in a dielectric layer deposited onn-type layer 1050 using similar photolithographic techniques or othertechniques. For example, micro-lens arrays may be formed in a polymerlayer through thermal reflowing of the polymer layer that is patternedusing a binary mask. The micro-lens arrays in the polymer layer may beused as the secondary optical components or may be used as the etch maskfor transferring the profiles of the micro-lens arrays into a dielectriclayer or a semiconductor layer. The dielectric layer may include, forexample, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. In someembodiments, a micro-LED 1070 may have multiple corresponding secondaryoptical components, such as a micro-lens and an anti-reflection coating,a micro-lens etched in the semiconductor material and a micro-lensetched in a dielectric material layer, a micro-lens and a grating, aspherical lens and an aspherical lens, and the like. Three differentsecondary optical components are illustrated in FIG. 10 to show someexamples of secondary optical components that can be formed onmicro-LEDs 1070, which does not necessary imply that different secondaryoptical components are used simultaneously for every LED array.

FIG. 11 illustrates an example of a display device 1100 that includesthree arrays of LEDs that are coupled to a waveguide. The LEDs may beμLEDs. As shown in the top portion of FIG. 11, display device 1100 mayinclude die 1105, die 1110, and die 1115, which are mounted on abackplane 1122 via I/O bumps 1150. The dies 1105, 1110, and 1115 may beLED dies. Die 1105 may include an array of LEDs that are configured toemit red light, such as the red light emitters 512 shown in FIG. 5A. Die1110 may include an array of LEDs that are configured to emit greenlight, such as the green light emitters 514 shown in FIG. 5A. Die 1115may include an array of LEDs that are configured to emit blue light,such as the blue light emitters 516 shown in FIG. 5A. Each of theprojection optics 520 shown in FIG. 5A may be a lens that collimates thelight from the red light emitters 512, the green light emitters 514, andthe blue light emitters 516, respectively. The dies 1105, 1110, and 1115are configured to be co-planar along the z direction, but may bestaggered in any suitable configuration along the x direction and/or they direction. A first additional layer 1125, such as a first fan-outcircuit, may be provided between die 1105 and the backplane 1122. Asecond additional layer 1130, such as a second fan-out circuit, may beprovided between die 1110 and the backplane 1122. A third additionallayer 1135, such as a third fan-out circuit, may be provided between die1115 and the backplane 1122. The backplane 1122 may have driver andgraphics functions. The backplane 1122 may include a backplane die 1120that is positioned underneath at least one of the dies 1105, 1110, or1115, and that drives the dies 1105, 1110, and 1115.

The bottom portion of FIG. 11 shows a cross-section taken along line A-Alabeled in the top portion of FIG. 11. As shown in the bottom portion ofFIG. 11, a redistribution layer 1140 may be provided to allow the dies1105, 1110, and 1115 to interface with the backplane 1122 such that thedies 1105, 1110, and 1115 are not required to be positioned entirely orexactly on top of the backplane 1122. Additional I/O bumps 1145 may beprovided on the underside of the backplane 1122 in order to provide aconnection between the backplane 1122 and a sensor aggregation chip (notshown), and to supply power to the integrated circuit, including thedies 1105, 1110, and 1115.

FIGS. 12, 13A, and 13B illustrate examples of methods for aligningcollimating lenses with dies that are positioned on a backplane. Themethods may be used to align the collimating lenses with the dies withinseveral microns in the x-y plane. The alignment may prevent walk-off ofthe light beams that are transmitted by the collimating lenses.

In a first method shown in FIG. 12, photolithography is used to form twosets of contact pads on the top surface of a backplane 1220 of a displaydevice 1200. The two sets of contact pads may be made of metal. The twosets of contact pads may be formed simultaneously or in sequence.Forming the two sets of contact pads by photolithography may ensure ahigh precision alignment of the collimating lenses with the dies. Insome examples, forming the two sets of contact pads simultaneously mayensure that the two sets of contact pads are automatically aligned witheach other. The alignment may also be achieved by controlling theoperation of the photolithography system. The first set of contact pads1255 are formed to provide electrical contact between the backplane 1220and die 1205, die 1210, and die 1215. During assembly, each of die 1205,die 1210, and die 1215 is positioned on a respective first subset of thefirst set of contact pads 1255, and may be connected to the backplane1220 via the respective first subset of the first set of contact pads1255. Further, a plurality of alignment balls 1265 are positioned on thesecond set of contact pads 1260. Each of the alignment balls 1265 may bemade of a fusible material such as solder. The same fusible material maybe used to connect the dies 1205, 1210, and 1215 with the first set ofcontact pads 1255.

The alignment balls 1265 may have a variety of shapes. In some examples,each of the alignment balls 1265 may have a spherical shape, and may bereferred to as spherical alignment balls. Each of the sphericalalignment balls may have a diameter between approximately 0.1 mm andapproximately 1.0 mm, and an aspect ratio of approximately 1:1. Forexample, each of the spherical alignment balls may have a diameter ofapproximately 0.3 mm +/−0.001 mm. The size of the spherical alignmentballs may be adjusted by controlling the amount of material used to formeach spherical alignment ball. A minimum of three spherical alignmentballs may be formed on the second set of contact pads 1260. In otherexamples, each of the alignment balls 1265 may have an oblong shape, andmay be referred to as oblong alignment balls. A minimum of two oblongalignment balls with orthogonal long axes may be formed on the secondset of contact pads 1260.

A first collimator assembly 1251 may be aligned with the display device1200 shown in FIG. 12. The first collimator assembly 1251 includes acollimating lens 1252, such as one of the projection optics 520 shown inFIG. 5A, for each of die 1205, die 1210, and die 1215. Further, thefirst collimator assembly 1251 includes a corresponding hole 1253 foreach of the alignment balls 1265 that are formed on the second set ofcontact pads 1260. In some examples, the holes 1253 may be formed byinjection molding of a plastic or polymer material of the firstcollimator assembly 1251. The holes 1253 may have a cylindrical shapewith a circular cross-section to match spherical alignment balls.Alternatively, the holes 1253 may have a cylindrical shape with anoblong cross-section to match oblong alignment balls.

After reflow of the fusible material, the lenses 1252 of the firstcollimator assembly 1251 are aligned with die 1205, die 1210, and die1215 by inserting the alignment balls 1265 into the corresponding holes1253 of the first collimator assembly 1251. The alignment may occur ineither direction (e.g., the alignment balls 1265 may be raisedvertically into the corresponding holes 1253, or the corresponding holes1253 may be lowered vertically around the alignment balls 1265). Each ofthe alignment balls 1265 may have a clearance of approximately 0.005 mmto 0.010 mm with respect to the corresponding holes 1253. The firstcollimator assembly 1251 may be secured in place with an adhesivebetween the first collimator assembly 1251 and the backplane 1220. Thedisplay device 1200 and the collimator assembly 1251 may be integratedto form a display projector.

In a second method shown in FIGS. 13A and 13B, photolithography is usedto form contact pads 1370 and etched openings 1375 on the top surface ofthe backplane 1320. The contact pads 1370 and the etched openings 1375may be formed simultaneously or in sequence.

Forming the contact pads 1370 and the etched openings 1375 byphotolithography may ensure a high precision alignment of thecollimating lenses with the dies. The contact pads 1370 are formed toprovide electrical contact between the backplane 1320 and die 1305, die1310, and die 1315. The contact pads 1370 may be made of metal. Duringassembly, each of die 1305, die 1310, and die 1315 is positioned on arespective subset of the contact pads 1370, and may be bonded to thebackplane 1320 via the respective subset of the contact pads 1370. Afusible material such as solder may be used to connect the dies 1305,1310, and 1315 with the contact pads 1370.

FIG. 13B shows additional details of an example of an opening 1375 andthe area 1380 surrounding the opening 1375. The opening 1375 may beetched through several layers of a redistribution layer (RDL). In theexample shown in FIG. 13B, the opening 1375 is etched through threelayers of metal 1385 and two layers of dielectric 1390. In this example,the opening 1375 is etched through a metal via 1395, such as a coppervia. In this example, the opening 1375 has metal sidewalls. In otherexamples, metal vias may be removed during the etching process, or theopenings 1375 may be etched directly through the RDL layer. The opening1375 may have a small depth and a large width. For example, the depthmay be approximately 30 μm and the width may be between approximately200 μm and approximately 500 μm.

A second collimator assembly 1351 may be aligned with the display device1300 shown in FIG. 13A. The second collimator assembly 1351 includes acollimating lens 1352, such as one of the projection optics 520 shown inFIG. 5A, for each of die 1305, die 1310, and die 1315. Further, thesecond collimator assembly 1351 includes a corresponding protrusion 1354for each of the openings 1375 that are etched on the top surface of thebackplane 1320. In some examples, the protrusions 1354 may be formed byinjection molding of a plastic or polymer material of the secondcollimator assembly 1351. The protrusions 1354 may have a cylindricalshape with a circular cross-section to match the circular cross-sectionof the openings 1375. The protrusions 1354 may have vertical sidewallsor sloped sidewalls.

After reflow of the fusible material, the lenses 1352 of the secondcollimator assembly 1351 are aligned with die 1305, die 1310, and die1315 by inserting the protrusions 1354 of the second collimator assembly1351 into the corresponding openings 1375. The alignment may occur ineither direction (e.g., the protrusions 1354 may be lowered verticallyinto the corresponding openings 1375, or the corresponding openings 1375may be raised vertically around the protrusions 1354). Each of theprotrusions 1354 may have a clearance of approximately 0.005 mm to 0.010mm with respect to the corresponding opening 1375. The second collimatorassembly 1351 may be secured in place with an adhesive between thesecond collimator assembly 1351 and the backplane 1320. The displaydevice 1300 and the collimator assembly 1351 may be integrated to form adisplay projector.

The alignment methods described herein may provide better accuracy ascompared with related art alignment methods. For example, related artmethods may use holes in a heat sink on which the backplane is mountedto align the heat sink with a PC board. The holes in the heat sink arealigned with matching holes in the PC board, and fasteners are insertedthrough both sets of holes. The heat sink is then clamped to the PCboard. This related art method provides a very coarse alignment, anddoes not align the dies with a specific feature. In contrast, thealignment methods described herein use high-precision lithography toform the features that are used to align the dies with the collimatinglenses.

FIG. 14 is a simplified block diagram of an example electronic system1400 of an example near-eye display (e.g., HMD device) for implementingsome of the examples disclosed herein. Electronic system 1400 may beused as the electronic system of an HMD device or other near-eyedisplays described above. In this example, electronic system 1400 mayinclude one or more processor(s) 1410 and a memory 1420. Processor(s)1410 may be configured to execute instructions for performing operationsat a number of components, and can be, for example, a general-purposeprocessor or microprocessor suitable for implementation within aportable electronic device. Processor(s) 1410 may be communicativelycoupled with a plurality of components within electronic system 1400. Torealize this communicative coupling, processor(s) 1410 may communicatewith the other illustrated components across a bus 1440. Bus 1440 may beany subsystem adapted to transfer data within electronic system 1400.Bus 1440 may include a plurality of computer buses and additionalcircuitry to transfer data.

Memory 1420 may be coupled to processor(s) 1410. In some embodiments,memory 1420 may offer both short-term and long-term storage and may bedivided into several units. Memory 1420 may be volatile, such as staticrandom access memory (SRAM) and/or dynamic random access memory (DRAM)and/or non-volatile, such as read-only memory (ROM), flash memory, andthe like. Furthermore, memory 1420 may include removable storagedevices, such as secure digital (SD) cards. Memory 1420 may providestorage of computer-readable instructions, data structures, programmodules, and other data for electronic system 1400. In some embodiments,memory 1420 may be distributed into different hardware modules. A set ofinstructions and/or code might be stored on memory 1420. Theinstructions might take the form of executable code that may beexecutable by electronic system 1400, and/or might take the form ofsource and/or installable code, which, upon compilation and/orinstallation on electronic system 1400 (e.g., using any of a variety ofgenerally available compilers, installation programs,compression/decompression utilities, etc.), may take the form ofexecutable code.

In some embodiments, memory 1420 may store a plurality of applicationmodules 1422 through 1424, which may include any number of applications.Examples of applications may include gaming applications, conferencingapplications, video playback applications, or other suitableapplications. The applications may include a depth sensing function oreye tracking function. Application modules 1422-1424 may includeparticular instructions to be executed by processor(s) 1410. In someembodiments, certain applications or parts of application modules1422-1424 may be executable by other hardware modules 1480. In certainembodiments, memory 1420 may additionally include secure memory, whichmay include additional security controls to prevent copying or otherunauthorized access to secure information.

In some embodiments, memory 1420 may include an operating system 1425loaded therein. Operating system 1425 may be operable to initiate theexecution of the instructions provided by application modules 1422-1424and/or manage other hardware modules 1480 as well as interfaces with awireless communication subsystem 1430 which may include one or morewireless transceivers. Operating system 1425 may be adapted to performother operations across the components of electronic system 1400including threading, resource management, data storage control and othersimilar functionality.

Wireless communication subsystem 1430 may include, for example, aninfrared communication device, a wireless communication device and/orchipset (such as a Bluetooth® device, an IEEE 802.11 device, a Wi-Fidevice, a WiMax device, cellular communication facilities, etc.), and/orsimilar communication interfaces. Electronic system 1400 may include oneor more antennas 1434 for wireless communication as part of wirelesscommunication subsystem 1430 or as a separate component coupled to anyportion of the system. Depending on desired functionality, wirelesscommunication subsystem 1430 may include separate transceivers tocommunicate with base transceiver stations and other wireless devicesand access points, which may include communicating with different datanetworks and/or network types, such as wireless wide-area networks(WWANs), wireless local area networks (WLANs), or wireless personal areanetworks (WPANs). A WWAN may be, for example, a WiMax (IEEE 802.16)network. A WLAN may be, for example, an IEEE 802.11x network. A WPAN maybe, for example, a Bluetooth network, an IEEE 802.15x, or some othertypes of network. The techniques described herein may also be used forany combination of WWAN, WLAN, and/or WPAN. Wireless communicationssubsystem 1430 may permit data to be exchanged with a network, othercomputer systems, and/or any other devices described herein. Wirelesscommunication subsystem 1430 may include a means for transmitting orreceiving data, such as identifiers of HMD devices, position data, ageographic map, a heat map, photos, or videos, using antenna(s) 1434 andwireless link(s) 1432. Wireless communication subsystem 1430,processor(s) 1410, and memory 1420 may together comprise at least a partof one or more of a means for performing some functions disclosedherein.

Embodiments of electronic system 1400 may also include one or moresensors 1490. Sensor(s) 1490 may include, for example, an image sensor,an accelerometer, a pressure sensor, a temperature sensor, a proximitysensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a modulethat combines an accelerometer and a gyroscope), an ambient lightsensor, or any other similar module operable to provide sensory outputand/or receive sensory input, such as a depth sensor or a positionsensor. For example, in some implementations, sensor(s) 1490 may includeone or more inertial measurement units (IMUs) and/or one or moreposition sensors. An IMU may generate calibration data indicating anestimated position of the HMD device relative to an initial position ofthe HMD device, based on measurement signals received from one or moreof the position sensors. A position sensor may generate one or moremeasurement signals in response to motion of the HMD device. Examples ofthe position sensors may include, but are not limited to, one or moreaccelerometers, one or more gyroscopes, one or more magnetometers,another suitable type of sensor that detects motion, a type of sensorused for error correction of the IMU, or any combination thereof. Theposition sensors may be located external to the IMU, internal to theIMU, or any combination thereof. At least some sensors may use astructured light pattern for sensing.

Electronic system 1400 may include a display module 1460. Display module1460 may be a near-eye display, and may graphically present information,such as images, videos, and various instructions, from electronic system1400 to a user. Such information may be derived from one or moreapplication modules 1422-1424, virtual reality engine 1426, one or moreother hardware modules 1480, a combination thereof, or any othersuitable means for resolving graphical content for the user (e.g., byoperating system 1425). Display module 1460 may use LCD technology, LEDtechnology (including, for example, OLED, ILED, μ-LED, AMOLED, TOLED,etc.), light emitting polymer display (LPD) technology, or some otherdisplay technology.

Electronic system 1400 may include a user input/output module 1470. Userinput/output module 1470 may allow a user to send action requests toelectronic system 1400. An action request may be a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.User input/output module 1470 may include one or more input devices.Example input devices may include a touchscreen, a touch pad,microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, agame controller, or any other suitable device for receiving actionrequests and communicating the received action requests to electronicsystem 1400. In some embodiments, user input/output module 1470 mayprovide haptic feedback to the user in accordance with instructionsreceived from electronic system 1400. For example, the haptic feedbackmay be provided when an action request is received or has beenperformed.

Electronic system 1400 may include a camera 1450 that may be used totake photos or videos of a user, for example, for tracking the user'seye position. Camera 1450 may also be used to take photos or videos ofthe environment, for example, for VR, AR, or MR applications. Camera1450 may include, for example, a complementary metal-oxide-semiconductor(CMOS) image sensor with a few millions or tens of millions of pixels.In some implementations, camera 1450 may include two or more camerasthat may be used to capture 3-D images.

In some embodiments, electronic system 1400 may include a plurality ofother hardware modules 1480. Each of other hardware modules 1480 may bea physical module within electronic system 1400. While each of otherhardware modules 1480 may be permanently configured as a structure, someof other hardware modules 1480 may be temporarily configured to performspecific functions or temporarily activated. Examples of other hardwaremodules 1480 may include, for example, an audio output and/or inputmodule (e.g., a microphone or speaker), a near field communication (NFC)module, a rechargeable battery, a battery management system, awired/wireless battery charging system, etc. In some embodiments, one ormore functions of other hardware modules 1480 may be implemented insoftware.

In some embodiments, memory 1420 of electronic system 1400 may alsostore a virtual reality engine 1426. Virtual reality engine 1426 mayexecute applications within electronic system 1400 and receive positioninformation, acceleration information, velocity information, predictedfuture positions, or any combination thereof of the HMD device from thevarious sensors. In some embodiments, the information received byvirtual reality engine 1426 may be used for producing a signal (e.g.,display instructions) to display module 1460. For example, if thereceived information indicates that the user has looked to the left,virtual reality engine 1426 may generate content for the HMD device thatmirrors the user's movement in a virtual environment. Additionally,virtual reality engine 1426 may perform an action within an applicationin response to an action request received from user input/output module1470 and provide feedback to the user. The provided feedback may bevisual, audible, or haptic feedback. In some implementations,processor(s) 1410 may include one or more GPUs that may execute virtualreality engine 1426.

In various implementations, the above-described hardware and modules maybe implemented on a single device or on multiple devices that cancommunicate with one another using wired or wireless connections. Forexample, in some implementations, some components or modules, such asGPUs, virtual reality engine 1426, and applications (e.g., trackingapplication), may be implemented on a console separate from thehead-mounted display device. In some implementations, one console may beconnected to or support more than one HMD.

In alternative configurations, different and/or additional componentsmay be included in electronic system 1400. Similarly, functionality ofone or more of the components can be distributed among the components ina manner different from the manner described above. For example, in someembodiments, electronic system 1400 may be modified to include othersystem environments, such as an AR system environment and/or an MRenvironment.

The methods, systems, and devices discussed above are examples. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods described may be performed in an order different from thatdescribed, and/or various stages may be added, omitted, and/or combined.Also, features described with respect to certain embodiments may becombined in various other embodiments. Different aspects and elements ofthe embodiments may be combined in a similar manner. Also, technologyevolves and, thus, many of the elements are examples that do not limitthe scope of the disclosure to those specific examples.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, systems, structures, and techniques have been shown withoutunnecessary detail in order to avoid obscuring the embodiments. Thisdescription provides example embodiments only, and is not intended tolimit the scope, applicability, or configuration of the invention.Rather, the preceding description of the embodiments will provide thoseskilled in the art with an enabling description for implementing variousembodiments. Various changes may be made in the function and arrangementof elements without departing from the spirit and scope of the presentdisclosure.

Also, some embodiments were described as processes depicted as flowdiagrams or block diagrams. Although each may describe the operations asa sequential process, many of the operations may be performed inparallel or concurrently. In addition, the order of the operations maybe rearranged. A process may have additional steps not included in thefigure. Furthermore, embodiments of the methods may be implemented byhardware, software, firmware, middleware, microcode, hardwaredescription languages, or any combination thereof. When implemented insoftware, firmware, middleware, or microcode, the program code or codesegments to perform the associated tasks may be stored in acomputer-readable medium such as a storage medium. Processors mayperform the associated tasks.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized or special-purpose hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

With reference to the appended figures, components that can includememory can include non-transitory machine-readable media. The term“machine-readable medium” and “computer-readable medium” may refer toany storage medium that participates in providing data that causes amachine to operate in a specific fashion. In embodiments providedhereinabove, various machine-readable media might be involved inproviding instructions/code to processing units and/or other device(s)for execution. Additionally or alternatively, the machine-readable mediamight be used to store and/or carry such instructions/code. In manyimplementations, a computer-readable medium is a physical and/ortangible storage medium. Such a medium may take many forms, including,but not limited to, non-volatile media, volatile media, and transmissionmedia. Common forms of computer-readable media include, for example,magnetic and/or optical media such as compact disk (CD) or digitalversatile disk (DVD), punch cards, paper tape, any other physical mediumwith patterns of holes, a RAM, a programmable read-only memory (PROM),an erasable programmable read-only memory (EPROM), a FLASH-EPROM, anyother memory chip or cartridge, a carrier wave as described hereinafter,or any other medium from which a computer can read instructions and/orcode. A computer program product may include code and/ormachine-executable instructions that may represent a procedure, afunction, a subprogram, a program, a routine, an application (App), asubroutine, a module, a software package, a class, or any combination ofinstructions, data structures, or program statements.

Those of skill in the art will appreciate that information and signalsused to communicate the messages described herein may be representedusing any of a variety of different technologies and techniques. Forexample, data, instructions, commands, information, signals, bits,symbols, and chips that may be referenced throughout the abovedescription may be represented by voltages, currents, electromagneticwaves, magnetic fields or particles, optical fields or particles, or anycombination thereof.

Terms, “and” and “or” as used herein, may include a variety of meaningsthat are also expected to depend at least in part upon the context inwhich such terms are used. Typically, “or” if used to associate a list,such as A, B, or C, is intended to mean A, B, and C, here used in theinclusive sense, as well as A, B, or C, here used in the exclusivesense. In addition, the term “one or more” as used herein may be used todescribe any feature, structure, or characteristic in the singular ormay be used to describe some combination of features, structures, orcharacteristics. However, it should be noted that this is merely anillustrative example and claimed subject matter is not limited to thisexample. Furthermore, the term “at least one of” if used to associate alist, such as A, B, or C, can be interpreted to mean any combination ofA, B, and/or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.

Further, while certain embodiments have been described using aparticular combination of hardware and software, it should be recognizedthat other combinations of hardware and software are also possible.Certain embodiments may be implemented only in hardware, or only insoftware, or using combinations thereof. In one example, software may beimplemented with a computer program product containing computer programcode or instructions executable by one or more processors for performingany or all of the steps, operations, or processes described in thisdisclosure, where the computer program may be stored on a non-transitorycomputer readable medium. The various processes described herein can beimplemented on the same processor or different processors in anycombination.

Where devices, systems, components or modules are described as beingconfigured to perform certain operations or functions, suchconfiguration can be accomplished, for example, by designing electroniccircuits to perform the operation, by programming programmableelectronic circuits (such as microprocessors) to perform the operationsuch as by executing computer instructions or code, or processors orcores programmed to execute code or instructions stored on anon-transitory memory medium, or any combination thereof. Processes cancommunicate using a variety of techniques, including, but not limitedto, conventional techniques for inter-process communications, anddifferent pairs of processes may use different techniques, or the samepair of processes may use different techniques at different times.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that additions, subtractions, deletions, and other modificationsand changes may be made thereunto without departing from the broaderspirit and scope as set forth in the claims. Thus, although specificembodiments have been described, these are not intended to be limiting.Various modifications and equivalents are within the scope of thefollowing claims.

1. A method comprising: using lithography to form a first plurality of contact pads on a backplane and a second plurality of contact pads on the backplane; bonding a plurality of dies to the first plurality of contact pads, wherein each of the plurality of dies comprises a plurality of light emitting diodes; forming a first plurality of features on the second plurality of contact pads; and aligning a plurality of lenses on an assembly with the plurality of dies by coupling a second plurality of features on the assembly with the first plurality of features on the second plurality of contact pads.
 2. The method of claim 1, wherein the first plurality of features are balls comprising a fusible material and the second plurality of features are recesses in the collimator assembly.
 3. The method of claim 2, wherein each of the balls has a spherical shape.
 4. The method of claim 2, wherein each of the balls has an oblong shape.
 5. The method of claim 1, wherein each of the plurality of lenses is a collimating lens.
 6. The method of claim 1, wherein the first plurality of contact pads and the second plurality of contact pads are formed simultaneously.
 7. A method comprising: using lithography to form a plurality of contact pads on a backplane and a plurality of openings in the backplane; bonding a plurality of dies to the plurality of contact pads, wherein each of the plurality of dies comprises a plurality of light emitting diodes; and aligning a plurality of lenses on an assembly with the plurality of dies by coupling a plurality of features on the assembly with the plurality of openings in the backplane.
 8. The method of claim 7, wherein the plurality of features are protrusions from the collimator assembly.
 9. The method of claim 7, wherein the plurality of openings extend through a redistribution layer of the backplane.
 10. The method of claim 7, wherein the backplane further comprises a metal sidewall for each of the plurality of openings.
 11. The method of claim 7, wherein each of the plurality of lenses is a collimating lens.
 12. The method of claim 6, wherein the plurality of contact pads and the plurality of openings are formed simultaneously.
 13. A display projector comprising: a display device comprising: a backplane; a plurality of dies, wherein each die of the plurality of dies comprises a plurality of light emitting diodes, and each die of the plurality of dies is connected to the backplane; and a first plurality of features on the backplane; a collimator assembly comprising: a plurality of lenses; and a second plurality of features on the collimator assembly; wherein the first plurality of features on the backplane are coupled with the second plurality of features on the collimator assembly such that the plurality of dies are aligned with the plurality of lenses.
 14. The display projector of claim 13, wherein the first plurality of features are balls comprising a fusible material and the second plurality of features are recesses in the collimator assembly.
 15. The display projector of claim 14, wherein each of the balls has a spherical shape.
 16. The display projector of claim 14, wherein each of the balls has an oblong shape.
 17. The display projector of claim 13, wherein the first plurality of features are openings in the backplane and the second plurality of features are protrusions from the collimator assembly.
 18. The display projector of claim 17, wherein the openings extend through a redistribution layer of the backplane.
 19. The display projector of claim 17, wherein the backplane further comprises a metal sidewall for each of the openings. 